Halogenated elastomers

There have been other approaches to obtaining rubber/metal adhesion besides primers or additives consisting of phenolics or epoxies plus halogenated elastomers. For example, carboxylated polymers (olefins and diolefins copolymerized with acrylic acid monomers) have shown excellent adhesion to metals. Very little carboxyl is necessary, and polymers with carboxyl contents as low as 0.1% show good adhesion when laminated to bare steel. When these materials possess... 

The processes of washing, neutralisation, and stabilisation of the halogenated elastomer also occur in turbulent flow motion by the introduction of an appropriate agent. 

The continuous technological process of halogenated elastomer production, using small-sized tubular turbulent reactors, may be realised by a more compact flow sheet (Figure 5.6) [17]. 

Halogenated elastomers are often cured by metal oxides, in combination with other ingredients. These include chlorosulfonated polyethylene, chloro- and bromo-butyl, and neoprene. 

The vast majority of rubber compounds use zinc oxide as an activator. In the case of rubber compounds based on halogenated elastomers such as polychloroprene, the zinc oxide functions as the vulcanizing agent itself and is even more critical. 

The temperature at which the magnesium oxide is calcined is important for its performance in rubber. The calcined MgO product must have sufficient activity to be an effective acid acceptor for use in halogenated elastomer compounds. The light burned grades that are calcined between 700 and 1000 °C usually work well for rubber applications. 

Halogenated elastomer Silicone Epoxy Polyester diator components... 

Metal oxides, usually zinc oxide but on occasion lead oxide for improved water resistance, are used as crosslinking agents for halogenated elastomers such as neoprene, halobutyl rubber, and chlorosulfonated polyethylene. The metal oxide abstracts the allylic halogen of adjacent polymer chains to form an oxygen crosslink plus the metal chloride salt. 

Uses Processing aid for nat. and syn. rubber, e g., NR, SBR, and EPDM (except halogenated elastomers), esp. for extruded compds., but also for transfer and in], molding tiller dispersant cure activator flow aid, wetting agent, vise, reducer, vise, stabilizer in silica compds. food-contact rubber articles Regulatory FDA 21CFR 177.2600 and BGA approved Properties YIsh. pastilles sp.gr. 1.10 drop pt. 96 C 8.5% Zn Use Level 1-3 phr... 

Flame and Smoke Retardants. Molybdenum compounds are used extensively as flame retardants (qv) (93,94) in the formulation of halogenated polymers such as PVC, polyolefins, and other plastics elastomers and fabrics. An incentive for the use of molybdenum oxide and other molybdenum smoke and flame retardants is the elimination of the use of arsenic trioxide. Although hydrated inorganics are often used as flame retardants, and thought to work by releasing water of crystallization, anhydrous molybdenum oxides are effective. Presumably the molybdenum oxides rapidly form... 

Meta.1 Oxides. Halogen-containing elastomers such as polychloropreae and chlorosulfonated polyethylene are cross-linked by their reaction with metal oxides, typically ziac oxide. The metal oxide reacts with halogen groups ia the polymer to produce an active iatermediate which then reacts further to produce carbon—carbon cross-links. Ziac chloride is Hberated as a by-product and it serves as an autocatalyst for this reaction. Magnesium oxide is typically used with ZnCl to control the cure rate and minimize premature cross-linking (scorch). 

Grades of polyisobutylene, butyl mbber, halogenated butyl mbber, and partially cross-linked isobutylene—isopiene—divinylbenzene terpolymer have been developed to meet specific processing and property needs. Recently, two new polyisobutylene-based elastomers have been developed. One is now available commercially as Exxon SB Butyl Polymers (32) and the other is under market development as Exxon bromo XP-50. 

Two elastomers have been commercialized with unique property profiles. One has fluoroalkoxy substituents that provide resistance to many fluids, especially to hydrocarbons. This material also has a broad use temperature range and useful dynamic properties. Aryloxy substituents provide flame retardant materials without halogens. 

Properties and Applieations. Aryloxyphosphazene elastomers using phenoxy and J-ethylphenoxy substituents have found interest in a number of appHcations involving fire safety. This elastomer has a limiting oxygen index of 28 and contains essentially no halogens. It may be cured using either peroxide or sulfur. Peroxide cures do not require the allyhc cute monomer. Gum physical properties are as follows (17) ... 

Other thermoplastic elastomer combiaations, ia which the elastomer phase may or may not be cross-linked, include blends of polypropylene with nitrile (30,31), butyl (33), and natural (34) mbbers, blends of PVC with nitrile mbber (35,36), and blends of halogenated polyolefins with ethylene interpolymers (29). Collectively, thermoplastic elastomers of this type ate referred to herein as hard polymer/elastomer combinations. Some of the more important examples of the various types are shown in Table 3. 

The results obtained by Kuila et al. and Acharya et al. [63,64] from the EVA elastomer blended with lamellar-like Mg-Al layered double hydroxide (LDH) nanoparticles demonstrate that MH nanocrystals possess higher flame-retardant efficiency and mechanical reinforcing effect by comparison with common micrometer grade MH particles. Kar and Bhowmick [65] have developed MgO nanoparticles and have investigated their effect as cure activator for halogenated mbber. The results as shown in Table 4.2 are promising. 

Isobutylene-based elastomers include HR, the copolymer of isobutylene and isoprene, halogenated HR, star-branched versions of these polymers, and the terpolymer isobutylene-p-methylene styrene-bromo-p-methyl styrene (BIMS). A number of recent reviews on isobutylene-based elastomers are available [33-35]. 

The most prevalent approach to achieve long-lasting and nonstaining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The ozone-resistant polymer must be used in sufficient concentration (minimum 25 phr) and must also be sufficiently dispersed to form domains that effectively block the continuous propagation of an ozone-initiated crack through the diene rubber phase within the compound. Elastomers such as ethylene-propylene-diene terpolymers, halogenated butyl mbbers, or brominated isobutylene-co-para-methylstyrene elastomers have been proposed in combination with NR and/or butadiene rubber. 

Femandez-Garcfa J.C., Orgiles-Barcelo, and A.C., Martm-Martmez J.M., 1991, Halogenation of styrene-butadiene rubber to improve its adhesion to polyurethanes, J. Adhes. Sci Technol, 5, 1065-1080. Oldfield D. and Symes T.E.F., 1983, Surface modification of elastomers for bonding, J. Adhes., 16, 77-96. Pastor-Bias M.M., Ferrandiz-Gomez T.P., and Martm-Martmez J.M., 2000, Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroisocyanuric acid in different solvents, J. Adhes. Sci. Technol, 14, 561-581. 

Polv(Arvloxyphosphazene) Elastomers. Poly(aryloxyphosphazene) elastomers, III, prepared by the reaction of chloropolymer with mixed phenoxides, offer excellent fire resistance without the incorporation of halogens in the polymer or as an additive. In addition, in a fire situation smoke evolution from these polymers... 

Poly(aryloxyphosphazene) elastomers offer outstanding fire resistance without the presence of halogen. In a fire these elastomers produce low levels of smoke as well as low toxicity and non-corrosive off-gases. 

Chemical reactions are used to modify existing polymers, often for specialty applications. Although of considerable importance for plastics, very few polymer reactions (aside from crosslinking) are important for elastomers. Chlorination and bromination of Butyl rubber to the extent of about one halogen atom per isoprene unit yields elastomers which are more easily crosslinked than Butyl rubber. Substitution occurs with rearrangement to yield an allylic halide structure... 

Fire Resistant Elastomers. The poly(aryloxyphosphazene) elastomers offer excellent fire resistance without incorporating halogen in the polymer or as an additive. These polymers are self-extinguishing in air and generate only moderate non-corrosive smoke and a minimum of toxic combustion products upon combustion (50-53). The poly(aryloxyphosphazene) elastomers (APN ) have excellent potential for applications such as... 

Many other crosslinking reactions are used in commercial applications. A variety of halogen-containing elastomers are crosslinked by heating with a basic oxide (e.g., MgO or ZnO) and a primary diamine [Labana, 1986 Schmiegel, 1979]. This includes poly(epichlorohydrin) (Sec. 7-2b-6) various co- and terpolymers of fluorinated monomers such as vinylidene fluoride, hexafluoropropene, perfluoro(methyl vinyl ether), and tetrafluoroethylene (Sec. 6-8e) and terpolymers of alkyl acrylate, acrylonitrile, and 2-chloroethyl vinyl ether (Sec. 6-8e). 

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